From 49cc665f76bd507780d832aab400609f7c8a5209 Mon Sep 17 00:00:00 2001
From: Zack Buhman <zack@buhman.org>
Date: Mon, 30 Dec 2024 10:54:28 -0600
Subject: [PATCH] implement checkcast

---
 c/execute.c          | 87 +++++++++++++++++++++++++++++++-------------
 p/CheckCastTest.java | 26 +++++++++++++
 2 files changed, 88 insertions(+), 25 deletions(-)
 create mode 100644 p/CheckCastTest.java

diff --git a/c/execute.c b/c/execute.c
index 83be34e..0748fb7 100644
--- a/c/execute.c
+++ b/c/execute.c
@@ -179,7 +179,41 @@ void op_castore(struct vm * vm)
 
 void op_checkcast(struct vm * vm, uint32_t index)
 {
-  assert(!"op_checkcast");
+  int32_t * objectref = (int32_t *)operand_stack_peek_u32(vm->current_frame, 1);
+  if (objectref == nullptr) {
+    return;
+  }
+
+  struct class_entry * index_class_entry =
+    class_resolver_lookup_class_from_class_index(vm->class_hash_table.length,
+                                                 vm->class_hash_table.entry,
+                                                 vm->current_frame->class_entry,
+                                                 index);
+
+  struct class_entry * class_entry = (struct class_entry *)objectref[0];
+  while (true) {
+    assert(class_entry != nullptr);
+    if (class_entry == index_class_entry) {
+      return;
+    }
+    if (class_entry->class_file->super_class == 0) {
+      break;
+    }
+
+    struct constant * class_constant = &class_entry->class_file->constant_pool[class_entry->class_file->super_class - 1];
+    assert(class_constant->tag == CONSTANT_Class);
+    struct constant * class_name_constant =  &class_entry->class_file->constant_pool[class_constant->class.name_index - 1];
+    assert(class_name_constant->tag == CONSTANT_Utf8);
+    print_utf8_string(class_name_constant);
+    debugf("\n");
+
+    // superclass lookup
+    class_entry = class_resolver_lookup_class_from_class_index(vm->class_hash_table.length,
+                                                               vm->class_hash_table.entry,
+                                                               class_entry,
+                                                               class_entry->class_file->super_class);
+  }
+  assert(!"ClassCastException");
 }
 
 void op_d2f(struct vm * vm)
@@ -1102,32 +1136,35 @@ void op_instanceof(struct vm * vm, uint32_t index)
   assert(index_class_entry != nullptr);
 
   int32_t * objectref = (int32_t *)operand_stack_pop_u32(vm->current_frame);
+  if (objectref == nullptr) {
+    operand_stack_push_u32(vm->current_frame, (uint32_t)false);
+    return;
+  }
+
   bool value = false;
-  if (objectref != nullptr) {
-    struct class_entry * class_entry = (struct class_entry *)objectref[0];
-    while (true) {
-      assert(class_entry != nullptr);
-      if (class_entry == index_class_entry) {
-        value = true;
-        break;
-      }
-      if (class_entry->class_file->super_class == 0) {
-        break;
-      }
-
-      struct constant * class_constant = &class_entry->class_file->constant_pool[class_entry->class_file->super_class - 1];
-      assert(class_constant->tag == CONSTANT_Class);
-      struct constant * class_name_constant =  &class_entry->class_file->constant_pool[class_constant->class.name_index - 1];
-      assert(class_name_constant->tag == CONSTANT_Utf8);
-      print_utf8_string(class_name_constant);
-      debugf("\n");
-
-      // superclass lookup
-      class_entry = class_resolver_lookup_class_from_class_index(vm->class_hash_table.length,
-                                                                 vm->class_hash_table.entry,
-                                                                 class_entry,
-                                                                 class_entry->class_file->super_class);
+  struct class_entry * class_entry = (struct class_entry *)objectref[0];
+  while (true) {
+    assert(class_entry != nullptr);
+    if (class_entry == index_class_entry) {
+      value = true;
+      break;
     }
+    if (class_entry->class_file->super_class == 0) {
+      break;
+    }
+
+    struct constant * class_constant = &class_entry->class_file->constant_pool[class_entry->class_file->super_class - 1];
+    assert(class_constant->tag == CONSTANT_Class);
+    struct constant * class_name_constant =  &class_entry->class_file->constant_pool[class_constant->class.name_index - 1];
+    assert(class_name_constant->tag == CONSTANT_Utf8);
+    print_utf8_string(class_name_constant);
+    debugf("\n");
+
+    // superclass lookup
+    class_entry = class_resolver_lookup_class_from_class_index(vm->class_hash_table.length,
+                                                               vm->class_hash_table.entry,
+                                                               class_entry,
+                                                               class_entry->class_file->super_class);
   }
   operand_stack_push_u32(vm->current_frame, (uint32_t)value);
 }
diff --git a/p/CheckCastTest.java b/p/CheckCastTest.java
new file mode 100644
index 0000000..661cee8
--- /dev/null
+++ b/p/CheckCastTest.java
@@ -0,0 +1,26 @@
+package p;
+
+class Animal {
+}
+
+class Cat extends Animal {
+}
+
+class Dog extends Animal {
+}
+
+class CheckCastTest {
+    public static boolean test() {
+        Dog d = new Dog();
+        Cat c = new Cat();
+        Animal da = d;
+        Animal ca = c;
+        Cat cc = (Cat)da;
+        //Cat cc = (Cat)ca;
+        return cc instanceof Cat;
+    }
+
+    public static void main() {
+        test();
+    }
+}